1. Area of the Art
The field of the invention involves dollies which are small trucks used to move motion picture cameras and more specifically a braking system to allow careful control of dolly motion.
2. Description of Related Art
In filming televisions or motion pictures it is frequently necessary to move the camera—often while filming is taking place. For example, the camera may be moved forwards towards the actors to transition from a distant view to a more close-up view. To achieve this movement the camera, the camera man and the assistant camera man (“focus puller”) ride on the dolly which is usually pulled or pushed by dolly operators or “dolly grips.” When the dolly is used on a smooth surface, it can be used with pneumatic wheels. When the surface is uneven or where special precision of motion is required, special tracks are put down for the dolly to run on.
Often the film director determines a precise mark on which the moving dolly is supposed to stop. Considering that a dolly with camera, camera man and focus puller can easily weigh in excess of 700 pounds, it is easy to imagine that smoothly stopping the dolly on the mark—particularly when running on low friction tracks—can be extremely difficult. It may be necessary to use multiple dolly grips to bring the dolly to rest.
There has been a tremendous amount of development and improvement of dolly design. Great attention has been paid to various lift beams and booms to alter camera elevation. For examples see U.S. Pat. No. 6,478,427 to Morris et al., U.S. Pat. No. 6,517,207 to Chapman and U.S. Pat. No. 6,579,016 to Chapman. In addition much attention has been paid to various steering mechanisms. When the dolly runs on pneumatic tires, it must be steered like any car or truck. When it runs on a track, the track takes care of steering. Similarly, great attention has been paid to various wheel conversion systems that allow a simple switch-over from pneumatic tires to tracks. For examples see U.S. Pat. No. 4,566,391 to Haberl et al which discloses a wheel system that switches from tires to track wheels and illustrates a steering device for the tires, and U.S. Pat. No. 5,609,108 to Chapman which illustrates a different system for converting between track wheels and tires.
Dolly tracks are either square (like rail road tracks) or round in cross-section. With a square track it is possible to operate the dolly with pneumatic tires running on the upper surfaces of the tracks (guidance wheels run along the inward-facing track surfaces to prevent the dolly from falling off the tracks. With a round track special track-wheels having a wheel groove (round in cross-section) are often used to keep the dolly on the track. More recently, the grooved wheels has been replaced by pairs of skateboard wheels with the axle of one wheel perpendicular to the second wheel so the wheels contact the track simultaneously, one wheel contacting the track's inward-facing surface and the other wheel contacting the track's outward-facing surface. The flat skateboard wheels have minimal areas of contact with the track so that friction is greatly reduced.
The prior art has not addressed the problem of bringing a moving dolly to a smooth and precise stop on a track. Some prior art dollies include braking systems for use with a pneumatic tire configuration. Most of the braking systems are intended only as a “wheel locks” or parking brakes to prevent inadvertent movement of the dolly when it is at rest. A precisely controllable brake for use with dollies operating on tracks.